FR2836001A1 - EMISSION AND REPRODUCTION OF STEREOPHONIC AUDIO SIGNALS - Google Patents

Abstract

A method and a device for transmitting and reproducing stereophonic audio signals are described. The method includes dividing a first channel and a second channel (11, 12) into two frequency bands, combining the lower frequency band signals of the two channels, and outputting the combined signals or signals. representative thereof, and higher frequency band signals of the two channels or representative signals thereof. The device comprises: a divider (13, 14) for dividing each of the two channels into two frequency bands, a combiner (15) for combining the lower frequency band signals of the two channels, and a transmitter for transmitting the combined signals or signals representative of these, and the higher frequency band signals of the two channels, or signals representative thereof.

Description

relative to the first surface and the second surface.

  Field of the Invention The present invention relates to methods and apparatus

  stereophonic audio signals.

  The present invention also relates to a device for

  s reproduction of stereophonic signals.

  State of the art The Bluetooth standard allows devices to communicate with each other over a wireless link with certain devices.

  defined channels consisting of three SCO channels at 64 kbits per second.

  Each channel may carry sampled audio signals having a bandwidth of 4 kHz with 8-bit samples. However, the 4 kHz bandwidth is considered to be unsuitable for use with portable high fidelity equipment, although it is considered sufficient to carry wireless signals. It is known to reduce the amount of digital data necessary to represent stereophonic sound signals, using encoders according to the MPEG-1 standard. The stereophonic signals reconstituted after MPEG-1 compression tend to be of very high quality. However, MPEG encoders and decoders are not cheap to manufacture and tend to have relatively high power consumption. As a result, it is desirable to avoid their use

  in portable equipment running on battery.

  Advantages of the invention According to a first aspect of the invention, there is provided a method for transmitting stereophonic audio signals, the method comprising: dividing each of two channels into two frequency bands, combining the band signals lower frequency of the two channels, and the transmission of the combined signals or signals representative thereof, and the higher frequency band signals of the two channels or

  of signals representative of these.

  According to another characteristic of the invention, the method further comprises combining each of the transmitted higher frequency band signals, or signals representative thereof, with

  s combined signals or signals representative of them.

  According to a second aspect of the invention, there is provided a method for transmitting stereophonic audio signals, the method comprising: dividing each of two channels into two frequency bands, combining the lower frequency band signals of the two channels, the downward frequency shift of the higher frequency band signals of the two channels, and the transmission of the combined signals or signals representative thereof, and signals shifted in frequency or

  s signals representative of these.

  According to another characteristic of the invention, the method further comprises the upward frequency shift of each of the

  signals shifted in frequency, or of signals representative of those

  this; and the combination of each of the resulting signals, with the signals

  o combined or representative signals of these.

  According to other features of the above method, the transmitting step comprises transmitting the signals on three channels of

  digital data and / or on a radio link. The process is essential

  as described herein with reference to the accompanying drawings.

  According to a third aspect of the invention, a device for transmitting stereophonic audio signals is created, the device comprising: a divider for dividing each of two channels into two frequency bands, a combiner for combining the band signals frequency of the two channels, and a transmitter for transmitting the combined signals or signals representative thereof, and signals

  frequency band of the two channels or signals

of these.

  According to another characteristic of the invention, the device

  tif further comprises a second combiner for combining the combined signals or signals representative thereof, with the higher frequency band signals representative of one of the channels, or

  signals representative thereof; and a third combiner for combining

  the combined signals transmitted, or signals representative thereof, with the higher frequency band signals of the other channel,

  or signals representative thereof.

  According to a fourth aspect of the invention, a provision is

  of stereophonic audio signals, the device includes

  nant: a divider to divide each of two channels into two frequency bands, a combiner to combine frequency band signals

  Lower frequency of the two channels, a frequency converter for

  frequency down the higher frequency band signals of the two channels, and a transmitter for transmitting the combined signals or signals representative thereof, and the frequency-shifted signals

  or signals representative thereof.

  According to another characteristic of the invention, the device further comprises another upconverter for shifting upwardly each of the frequency-shifted signals transmitted, or signals representative thereof; and a second combiner to combine each of the resulting signals, with the

  combined signals emitted or signals representative of them.

  According to other characteristics of the invention, in the transmission devices the transmitter comprises means for transmitting the signals on three digital channels, and / or the transmitter is a radio transmitter. According to a fifth aspect of the invention, a device for reproducing stereophonic audio signals is created, this device comprising means for receiving signals transmitted over three audio channels, means for combining the signals received on a first of the channels. , with the signals received on a second one of the channels, so as to provide a first channel output signal, and means for combining the signals received on the first of the channels, with the received signals o on a third channel, of way to provide a second signal of

output of channels.

  According to another characteristic of the invention, the reproducing device further comprises means for translating frequency signals received on the second and third of the channels; and means for providing the frequency translated signals to the combining means. Drawings Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which: - Figure 1 is a diagram illustrating the principle of the invention; and - Figures 2 and 3 are diagrams of a first embodiment

  and a second embodiment of the invention.

Description of the drawings

  3s Referring to Figure 1, it schematically represents a device 10 for transmitting stereophonic audio signals. The device comprises left and right audio channel inputs 11, 12 with a bandwidth of 8 kHz each. First and second signal splitters 13, 14 are each connected to one of the channel inputs. The first divider 13 transmits the lowest 4 kHz signal received from its left channel input 11 to an adder 15, and transmits the highest 4 kHz signal to a down converter.

  16. The second signal divider 14 transmits in the same way the signal

  4 kHz signal the lowest of the signals received by the right channel input, at another input of the summator 15, and transmits the signal at the most 4 kHz

  up to a second down converter 17. Down converters

  16, 17 each lower the received signals by 4 kHz, and provide these signals to a respective one of a first channel and a second wireless data channel 18, 19 to 64 kbits per second. The summator 15 sums the signals it receives and provides them to a third wireless data channel 20 at 64 kbits per second. Each of the data channels 18-20 therefore carries a digitized audio signal oc

  with a bandwidth between 0 Hz and 4 kHz.

  Stereophonic audio signals are reconstructed at a receiver end of the data channels 18-20. First and second upconverting converters 21, 22 are each connected to one of the data channels 18, 19. These upconverters move each 4 kHz upwardly, the frequency of the received signals, giving signals identical to those applied to converters

  respective down-converters 16, 17. The signals provided by the first converts

  In the same way, a second summator is the sum of the signals supplied. In the same way, a second summator is added to the signals received by the third data channel 20 in a second summer 23 and the result is supplied to a left channel output 24. by the second upconverter 22, with the signals received by the third data channel 20, and provides

  the result at a right channel output 26.

  This results in the transmission of 16 kHz audio signals on channels having a combined bandwidth of 12 kHz. This result is obtained without any reduction in the quality of the highest frequency signals, but at the expense of imprecise reproduction of the lower frequency signals. However, this is not considered a problem in many circumstances because, for most of the recorded music, it is unusual to find a significant difference.

  between the low frequency components of the left and right channels.

  In addition, the human ear is much less able to discern di-

  a low frequency sound, that of a high frequency sound, so that a human listener is unlikely to be able to determine a difference between the case where the device 10 is used and the case where it is not used. This applies to sounds reproduced by

  loudspeakers, only sounds reproduced by headphones.

  A similar implementation of the device 10 is represented at 30 in FIG. 2 in which the same numerical references are reused for the same elements. Referring to FIG. 2, the device 30 comprises, as first signal divider 13, a high-pass filter 31 and a low-pass filter 32. Each of the filters 31, 32 has a cut-off frequency of 4 kHz . The second signal divider 14 likewise comprises a second high pass filter 33 and a second low pass filter 34 also having cutoff frequencies of 4 kHz. The downconvertors 16, 17 are formed from a first mixer 35 and a second mixer 36 which are connected in common to a square wave oscillator 37 at 4 kHz. The outputs of the meters 35, 36 are filtered by respective low-pass filters 38, 39, each having a cut-off frequency of 4 kHz, to suppress the unwanted frequencies. The summator 15 is constituted by an am

  plifier 40 provided with a feedback resistor 41.

  At the receiver side, the upconverting converters 21, 22 are formed by respective mixers 42, 43 which are supplied together by a square wave oscillator 44 at 4 kHz. The mixers 42, 43 of the upconverters 21, 22 are followed by respective high-pass filters 45, 46 each having a cut-off frequency of 4 kHz. The summers 23, 25 are constituted by respective amplifiers 47, 48 provided with respective feedback resistors 49, 50. In this embodiment, the data channels 18-20 are Blue tooth audio channels. For this purpose, the device 10 comprises analog / digital converters (CAN), a modulator, a radio transmitter, a radio receiver, a demodulator and digital / analog converters (DACs), not shown. The signals transmitted on the data channels 18 are therefore not the signals provided by the filters 38, 39 and the somatrix 15. On the contrary, the transmitted signals are representative of the signals supplied by the filters 38, 39 and the summator 15. Signals representing 3s are processed on the receiver side to reconstruct the signals provided

  by the filters 38, 39 and the summator 15.

  A digital implementation of the device 10 is shown at 60 in Figure 3. The same numerical references that cel of Figure 1 are reused to designate the same elements. Referring to Figure 3, the device 60 includes left and right ADCs 61, 62. Each of these ADCs samples the received signals at its respective input 11, 12, and outputs 16 k-samples of those every second. A first digital signal processor (PSN) 63 is provided to receive the sampled signals from the left channel, to perform high pass filtering so as to suppress signals having a frequency below 4 kHz, to convert the result of 4 kHz down, and to low-pass the down-converted signals so as to suppress the signals having a frequency higher than 4 kHz. The signals provided by the first PSN 63 have a sampling rate of 8 kbits per second. A second PSN 64 performs the

  same functions on the signals provided by the right channel CAN 62.

  The samples provided by the left and right ADCs 61, 62 are also filtered by a high-pass filter to suppress signals having a frequency greater than 4 KHz by means of a respective third and fourth PSNs. , 66. Signals from the third and

  fourth NHPs are added to each other by a numerical summator.

  15 which provides output samples at 8 kbits per second. The signals provided by the first and second PSNs 63, 64 and by the summator

  are prepared to be broadcast on Bluetooth voice channels

  18-20, at 64 kilobits per second, using a device that is not

sented.

  At the receiving end, a device not represented demo-

  2s decodes the Bluetooth data transmitted, and returns them to three digital channels.

  separate 8 kbits per second. The signals received on the third data channel 20 are processed by a fifth PSN 67 which doubles their sampling rate. The signals received on the second channel 18 are processed by a sixth PSN 68 which is designed to convert the signals of o 4 kHz upwards, then to filter the result by a high-pass filter so as to eliminate the components having frequencies lower than 4 kHz. The result which consists of 16 kbit / s samples is supplied to the second summator 23. A seventh PSN 69 performs the same functions on the signals received by the second channel 19, and provides

  s5 samples at 16 kbits per second at the third summator 25. The

  The cond and third summers add the signals received from their respective PSNs 68, 69, to the signals provided by the fifth PSN 67, to give 16 kbit / s samples at their respective outputs. The summators 23, 25 are connected to their respective outputs 24,

26 by the respective NACs 70, 71.

  There are various embodiments. In one embodiment, analog signals are processed on the transmitter side, as in the embodiment of Fig. 2, and are digitally processed on the receiver side, as in the embodiment of Fig. 3. In another mode. embodiment, not shown, signals are processed numerically on the transmitter side, and analog signals are processed

on the receiving side.

  The use of Bluetooth SCO channels is not essential for the invention. Any suitable channel could be used,

  according to the bandwidth requirements. In addition, the division of

  higher frequencies from the lower frequency components, can be modified. When, for example, there are three channels at 6 kHz, stereo signals with a bandwidth of 12 kHz can be emitted by suppressing the lower 6 lUIz of each channel,

  summing these signals, and emitting the sum on a third

  second channel. In this case, the left and right channels each carry signals having a bandwidth of 6 kHz, and the third

  o channel carries signals with a bandwidth of 6 kHz.

R E V E N D I C AT IO N S

  1) A method for transmitting steroophonic audio signals, characterized in that it comprises: dividing each of two channels (11, 12) into two frequency bands; the combination of the lower frequency band signals of the two channels; and transmitting the combined signals or signals representative thereof, and the higher frequency band signals of the two channels, or

signals representative thereof.

  The method of claim 1, characterized in that it further comprises combining each of the higher transmitted frequency band signals, or signals representative thereof, with

  the combined signals or signals representative thereof.

  3) Method for transmitting stereophonic audio signals, characterized in that it comprises: dividing each of two channels (11, 12) into two frequency bands; the combination of the lower frequency band signals of the two channels; the downward frequency shift of the higher frequency band signals of the two channels; and transmitting the combined signals or signals representative thereof, and frequency-shifted signals or signals representative thereof. 4) Method according to claim 3, characterized in that it further comprises the upward frequency shift of each of the transmitted frequency offset signals, or signals representative thereof; and the combination of each of the resulting signals, with the signals com

  or representative signals thereof.

   Method according to one of the preceding claims,

  characterized in that the transmitting step comprises transmitting the signals over three channels of

numerical data (18, 19, 20J.

s

  6) Process according to any one of the preceding claims,

characterized in that

  the transmitting step comprises transmitting the signals over a radio link.

  o 7) Method for transmitting stereophonic audio signals, characterized in that

  it is essentially as described herein with reference to the accompanying drawings.

  8) Apparatus for transmitting stereophonic audio signals, characterized in that it comprises: a divider (13, 14) for dividing each of two channels (11, 12) into two frequency bands; a combiner or summator (15) for combining the lower frequency band signals of the two channels; and

  transmitter to transmit the combined signals or signals

  of these, and higher frequency band signals from

  two channels, or signals representative thereof.

  9) A device according to claim 8, characterized in that it further comprises: a second combiner (23) for combining the combined signals or signals representative thereof, with the representative higher frequency band signals one of the channels, or signals representative of them; and a third combiner (25) for combining the transmitted combined signals, or signals representative thereof, with the higher frequency band signals of the other channel, or representative signals

3s of these.

   Stereophonic audio signal transmission device, characterized in that it comprises: a divider (13, 14) for dividing each of two channels (11, 12) into two frequency bands; a combiner (15) for combining the lower frequency band signals of the two channels; a downconverter (16, 17) for down-shifting the higher frequency band signals of the two channels; and a transmitter for transmitting the combined signals or representative signals thereof, and the frequency shifted signals, or signals

representative of these.

  11) Device according to claim 10, characterized in that it further comprises: another up-converter (21, 22) for frequency shifting upwards each of the transmitted frequency offset signals, or signals representative of those -this; and a second combiner to combine each of the resulting signals, with

  the combined signals transmitted or signals representative thereof.

  12) Device according to any one of claims 8 to 11,

  characterized in that the transmitter comprises means for transmitting the signals on three

digital numbers (18, 19, 20).

  13) Device according to any one of claims 8 to 12,

characterized in that

the transmitter is a radio transmitter.

  14) Apparatus for reproducing stereophonic audio signals, characterized in that it comprises: means for receiving signals transmitted on three audio channels (18,

19, 20);

  means for combining the received signals on a first one of the channels with the signals received on a second of the channels so as to provide a first channel output signal; and means for combining the received signals on the first of the channels, with the signals received on a third of the channels, so as to provide

  a second channel output signal.

  15) Device according to claim 14, characterized in that it further comprises: means for translating frequency signals received on the second and third of the channels; and o means for providing the frequency-translated signals, to the means